In charging devices, for example exhaust-gas turbochargers, for internal combustion engines, so-called wastegate valves are used for regulating power, said wastegate valves controlling a bypass that circumvents the turbine wheel of the exhaust-gas turbocharger, in order to prevent any possible damage occurring to the exhaust-gas turbocharger if the exhaust-gas stream contains too much power. Poppet valves are usually used, the valve disc of which is pivoted by an adjusting lever, in order to open or close a bypass opening. In order to cope the changing temperatures and temperature gradients during implementation in an automobile, the connection between the valve disc and the adjusting lever has some play, thus allowing the valve disc to be properly adjoined to a valve seat. However, this leads to, for example, that the valve disc can move and thus rattle in the adjusting lever when the bypass valve is open. It is known from prior art that pre-stressing the valve disc in an axial direction retains the valve disc in an end position.
A disadvantage of such an embodiment is that if a warping due to thermal expan-sions needs to be balanced out by the play between adjusting lever and valve disc, the force has to be overcome by the spring. Consequently, the actuating forces needed to close the bypass valve are relatively high.
Such a valve device is known for example from DE 10 2010 043 147 A1. The valve disc is pre-tensioned in an axial direction relative to the adjusting lever by a spring-elastic tensioning element, whereby the valve disc is fixed in a predetermined position on the adjusting lever.
A turbocharger with a wastegate valve, in which the valve disc is pre-tensioned in an axial direction against the adjusting lever by a disc spring, is known from WO 2010/135104 A2.
WO 2014/011468 also discloses an exhaust-gas turbocharger with a wastegate valve, in which the valve disc is pre-tensioned against the adjusting lever by means of an annular spring element.
A valve device for an exhaust-gas turbocharger, which has a centring element, which centres a mandrel of the valve disc in a through opening of the adjusting lever, is known from DE 10 2011 076 361 A1.
Finally DE 10 2012 101 322 also discloses an exhaust-gas turbocharger with a wastegate valve in which a disc spring is provided, in order to axially pre-stress the valve disc relative to the adjusting lever.